Water
Management Plan, Lot 3, South West Highway Whitby
1
CONTENTS
1.0
Background
2
2.0
Site Description and Landform
2
3.0
Geology, Soils, and Earthworks
3
4.0
Pre &
Post Development Scenarios
4
5.0
Flood Levels and Displacement Impact
5
6.0
Impacts on Surface Drainage and Water Quality
6
Figures
Figures 1-14
Site Photographs
Figures 15-17
Water Management Diagrams
SJS TRIM - IN12/17340
OCM122.9/01/13
Water Management Plan, Lot 3, South West Highway Whitby
2
WATER ASSESSMENT AND MANAGEMENT
1.0
Background
Lot 3, South West Highway is proposed by WA Bluemetal to have a 10.3
hectare area
within the property have 3m of landform raising to the current existing profile, and
rehabilitation to either original pasture for grazing or returning the area to native
vegetation. The original proposal was submitted to the Shire of Serpentine – Jarrahdale
on 25
th
November 2011.
The Shire of Serpentine – Jarrahdale resolved at the Ordinary Council Meeting held on
25 June 2012 that a Water Management Plan be prepared and submitted to the
satisfaction of the Director Strategic Community Planning, which forms the basis of this
document.
A site investigation was conducted by James Della Bona on 3 July 2012 by walking all
of Lot 3 with an examination of the remnant vegetation in addition to an examination of
the local roads and views.
2.0
Site Description and Landform
The site lies near the base of the Darling Scarp, around 350m east of the South West
Highway Road Reserve.
Elevation of the land ranges from 85 metres AHD in the south western corner to 126
metres AHD along the access road to the east of the site.
A winter creek runs along the western and southern boundaries of the proposed
landform raising site.
The site is sloping at 1 : 16 vertical to horizontal on
the lower slopes, grading to 1 : 7
vertical to horizontal over the mid to upper slopes of the site.
The location of the landform raising has been determined on a number of parameters
including;
•
selecting areas where the slopes are less severe,
•
visual management is able to be managed,
•
selecting
sparsely vegetated areas, and
•
access and servicing issues are minimised
An existing winter creek is located along the western and southern portions of the site.
A contour drain is to be installed 50m up from the winter creeks to catch any
sedimentary runoff, and will be installed according to a suitable engineering design,
which captures water from upslope and provides for retention and infiltration of that
water.
SJS TRIM - IN12/17340
OCM122.9/01/13
Water Management Plan, Lot 3, South West Highway Whitby
3
3.0
Geology, Soils and Earthworks
The site lies on soils developed on weathered granite associated with the Darling
Scarp. On this site the soils are yellow brown stony soils of colluvial origin resting on
weathered granite saprolite and saprock.
The soils are of in situ and colluvial origin. That is they have
formed predominantly
from soil, clay, stone or granite and dolerite combined with minor gravel being washed
down slope to rest on the weathered granite basement.
The soils are yellow brown sandy and stony loam soils which become lighter with
depth. They are generally friable and well drained. The lower soil horizons are
sometimes saprolitic and contain weathered fragments of rock and freed minerals.
The location of the soils, on a slope
in a higher rainfall area, results in the soils being
free from any salinity issues. All soils are well drained because of the slopes.
Earthworks will be constrained to the previously indicated boundaries of the 10.3
hectare site.
No particular construction difficulties are envisaged, due to construction occurring in
the summer months which is when the properties of the material are the most
‘construction friendly’. Cut off drains will be installed for stormwater management.
One access road onto the site will be constructed to the lower end of the site, in
accordance with the construction methodology to build the landform from the creek
side heading up the hill.
The main risk during earthworks is the risk of soil movement during construction in
winter from runoff storm events. Management practices are the same as those on any
other sloping lot. The potential for soil removal through water erosion
will be mitigated
through normal construction practices.
The environmental impacts from development will be constrained within the boundaries
of the site, which minimises the risk of weed spread, dieback intrusion, waste water
disposal, erosion, clearing and visual impact affecting the other areas of the Darling
Scarp.
SJS TRIM - IN12/17340
OCM122.9/01/13